Left testicle has been hurting throughout the day. Not terrible pain, more so an aggravating pain. That side also feels a little tighter than the right. I did it last night, but wasn't that rough. I hope nothing is majorly wrong. What could it be?

DUDE... You have those testicles because you are a MAN. Don't get all squirly because of one day of pain. Wait at least a week and don't take directions to the doctor in the event that you do end up going.